Cleaning shoes are major subsections of agricultural harvesters. Cleaning shoes are generally constructed as a housing that encloses a fan and one or more reciprocating sieve assemblies. The fan generates a flow of air that passes upward through the sieve assembly as the sieve assembly reciprocates fore and aft. This airflow lifts material other than grain (MOG) such as chaff or dust and carries it rearward out of the agricultural harvester where it is deposited on the ground. The grain is dense enough that it resists this flow of air and is not carried rearward, but instead falls downward through the sieve assembly onto a pan that extends underneath the sieve assembly. A transverse conveyor in the pan carries the grain to one side of the agricultural harvester, and a vertical conveyor carries the grain upward and into a grain tank or reservoir located at the top of the agricultural harvester.
To assist the air in separating the grain from the MOG, the sieve assembly is reciprocated in a generally horizontal plane. The speed of reciprocation is on the order of 300 cycles per minute. A typical sieve assembly comprises a generally rectangular frame that supports one or more lightweight sieves. The sieves are generally formed as dozens of very lightweight slats, each of which extends side to side with respect to the agricultural harvester. These lightweight slats are supported, in turn, in a second lightweight frame that is supported inside the generally rectangular frame. The slats can be positioned with respect to each other like slats in a Venetian blind. This permits the operator to vary the direction and intensity of air flow between the slats and therefore to vary the lifting and separating power of the air passing through the sieve assembly.
The sieve assembly is typically supported on hangers that extend generally vertically. The upper ends of the hangers are fixed to the chassis of the agricultural harvester. The lower ends of the hangers are fixed to the sieve assembly. A power source, such as a motor with a rotating shaft is connected to the hangers with an offset crank arrangement. As the motor rotates, the hangers are pivoted fore-and-aft at their lower ends to thereby shake the sieve assemblies. This reciprocation jostles the dirty grain falling on the sieve, spreads the grain out more evenly across the surface of the sieve and enhances the flow of air through the dirty grain.
Cleaning shoe design, and particularly the design of the reciprocating sieve assemblies, is a trade-off between strength, durability and weight. The cyclical loading of the reciprocating sieve assemblies tends to cause fasteners to loosen. For this reason, the reciprocating sieve assemblies are typically welded together. Unfortunately, the welds (if poorly made) are also prone to failure by metal fatigue.
What is needed, therefore, is a new configuration for a sieve assembly that weighs less and is more immune to the cyclical stresses.
It is an object of this invention to provide such an arrangement.